1. Field of the Invention (Technical Field)
The present invention relates generally to turbomachinery, particularly turbocharged internal combustion engines, and specifically relates to a turbine housing for improving the turbine efficiency characteristic.
2. Background Art
It is known in the general art of internal combustion engines to provide some system of turbocharging, whereby a turbine harnesses energy from exhaust gases to power a compressor. The compressor is then used to increase engine performance, typically by boosting the pressure of air supplied to the engine.
Nearly as important as engine performance is the need for cleaner exhausts. Most internal combustion engines are subject to regulations governing pollutant levels in engine emissions. “Stationary sources” such as internal combustion engine powered generators and the like, as well as motor vehicles, are required to maintain emissions of certain pollutants, such as CO and NOX, below legal limits. Pollution control, however, ideally is accomplished while compromising engine performance as little as possible.
One mode of reducing the emissions of internal combustion engines—regardless of whether the engine is turbocharged, but frequently when it is—is through exhaust gas recirculation (EGR). EGR involves the return to the engine's intake manifold of some portion of the engine exhaust. Exhaust gases are diverted from the exhaust manifold through a duct or conduit for delivery to the intake manifold, thereby allowing exhaust to be introduced to the combustion cycle, so that oxygen content is reduced, which in turn reduces the high combustion temperature that contributes to excessive NOX formation.
With the introduction of EGR systems on, for example, heavy-duty diesel engines, the desired turbine efficiency characteristic does not conform to conventional turbomachinery performance. Simply accepting classical turbomachinery turbine efficiency characteristic when using applicants' VNT™ brand of variable nozzle turbine turbocharger EGR System causes several effects, including: (1) Unacceptably high fuel consumption at certain engine operating speeds; (2) Unacceptably high turbocharger speed (i.e., turbocharger speeds which exceed acceptable limits using known production materials and processes); and (3) An inability to drive the EGR at all desires engine operating points.
Further, with the use of EGR systems in use on a heavy-duty diesel engine, the turbocharger “match” to the engine results in unusual turbocharger turbine wheel matching. In some instances, for example, the traditional or conventional wheel contour is removed from the design. This unusual machining of the turbine wheel may result in an increased difficulty in retaining the turbine wheel in the event the turbine wheel separates from the turbocharger shaft. In such an event, the turbine wheel will exit the turbine housing gas outlet at a substantially higher velocity and energy than in a similar circumstance with current turbocharger assembly designs.
Against the foregoing background, the present invention was developed. The turbine housing is modified to retain the wheel and to tailor the turbocharger turbine efficiency, thus addressing the deficiencies noted above. The scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.